Polysaccharides form a significant part of the market of aqueous polymers and have been developed for industrial applications because of their various functional properties. These polysaccharides are present in leaves, stems and roots of plants, seaweeds, animals, microorganisms, mycelia, insect chitins and the like. Natural polysaccharides extracted from plants and seaweeds were most applicable so far. As an example of these polysaccharides, starch of various plants, locust bean gum and guar gum extracted from roots of plants, agar, alginate extracted from seaweeds, and pectin extracted from plants may be mentioned (Whistler, R. L.: Industrial gums, Academic Press, New York (1959)). The quantity and the quality of the natural polysaccharides extracted from the plants greatly depend on the climate of the year. Thus, the costs, quality and supply of these polysaccharides are irregular, and the continuously increasing consumption of natural polysaccharides is not satisfied (Sandford, P.A.: Polysaccharides in Food (Blanshard, J. M. V. and Gaylord, N. G. ed) 8, 693-711 (1968)). Therefore, polysaccharides produced by microorganisms have been needed in order to overcome these problems.
Polysaccharides produced by microorganisms are of three types:
a. Exocellular polysaccharides of microorganisms in the form of a capsule or slime, PA1 b. Endocellular polysaccharides of microorganisms as an energy stock material in the microorganisms, and PA1 c. Polysaccharides constituting the cell wall.
Recently, due to the commercial success of dextran and xanthan gum among polysaccharides produced by microorganisms, the preparation of polysaccharides by microorganisms has become of increasing interest. Polysaccharides produced by microorganisms have the functional characteristics such as an emulsifying capacity, a viscosity increasing capacity, the capacities of stability and gelation, a water holding capacity, a film forming capacity, physiological activating capacity, an aggregation capacity, and the like. Therefore, investigations for various uses in the field of foods, cosmetics, oils and medicines have been conducted. Such uses are based on the inherent properties of polysaccharides. When the polysaccharides are produced by the fermentation of microorganisms, they have numerous advantages such as control of the quantity and the quality, control of the degree of synthesis by controlling the fermentation conditions, easy availability of cheap and plentiful raw materials, productivity with a high yield by continuous culture, control of the amount of production according to the market circumstances, and the like.
As microorganisms capable of producing polysaccharides, bacteria such as Agrobacter, Alcaligenes, Arthrobacter, Azotobacter, Bacillus, Pseudomonas and Klebsiella; yeasts such as Hansenula and Rhodotolura; and molds such as Pullularia, Rhizobium and Aspergillus are known. Investigations for the preparation of the polysaccharides by microorganisms have been continuously made since a few of them are applicable in the industries, and polysaccharides having new structures and properties are thus required.
To produce microbial polysaccharides, first of all, microorganisms having the desired characteristics are separated from nature, culture conditions to produce polysaccharides are studied with the separated strains, and then the studies must be made with regard to the purification of polysaccharides from culture medium, and their stability and applicability.